1. Field of the Invention
The present invention relates to a method for drying a coating film, and more specifically, to a method for drying a coating film for a thermal-developable light-sensitive material that uses an SBR (styrene-butadiene copolymer)-based binder and is difficult to be cured.
2. Description of the Related Art
In recent years, in the fields of medical diagnostic films and photoengraving films, the reduction of the quantities of treated waste liquids have strongly been demanded from the point of view of environmental preservation and space saving. In such a circumstance, technology related to thermal-developable light-sensitive materials has been desired for medical diagnostic films and photoengraving films that can be exposed efficiently using a laser image setter or a laser imager, and can form clear black images having high resolution and sharpness. The thermal-developable light-sensitive materials have advantages of providing a thermal developing system that needs no solvent-based chemicals for processing, can be used easily, and does not damage environment.
Coating liquids for light-sensitive materials can roughly be classified into coating liquids for silver halide photographic light-sensitive materials that use gelatin-based binders, and coating liquids for the above-described thermal-developable light-sensitive materials that use polymer-latex-based, for example, SBR (styrene-butadiene copolymer)-based binders. After coating a support with these coating liquids for light-sensitive materials to form a coating film, it is need to supply drying air to the coating film to dry the coating film.
However, the coating films using gelatin-based binders have characteristics of being cured easily; while the coating films using polymer-latex-based, for example, SBR (styrene-butadiene copolymer)-based binders have characteristics of being difficult to cure. Therefore, the coating films for silver halide photographic light-sensitive materials are difficult to produce liquid scattering by drying air; while the coating films for thermal-developable light-sensitive materials easily produce liquid scattering by drying air. As a result, the coating films for thermal-developable light-sensitive materials have disadvantage of difficulty to obtain good surface condition of coating films, and of easily lowering photographic performance.
The present invention has been worked out taking such situations into account, and the object of the present invention is to provide a method for drying a coating film for a thermal-developable light-sensitive material that can prevent liquid scattering by drying air during drying the coating film for the thermal-developable light-sensitive material; and can achieve good surface condition of the coating film, and good photographic performance.
In order to achieve the above-described object, the present invention is characterized in a method for drying, with drying air in a drying process, a coating film in manufacture of thermal-developable light-sensitive material formed by coating with a coating liquid that contains an organic silver salt, a reducer for silver ions, a polymer latex, and silver halide particles to a support being conveyed in a coating process, wherein: the drying process comprises: a chilling-zone step for cooling the coating film with cold air; a plane air cushion drying step for a first-stage drying of the coating film in a non-contact state while floating and supporting the support by supplying a hot drying air of a predetermined wind velocity to both sides of the support; a helical air cushion drying step for a second-stage drying of the coating film in a non-contact state while helically winding the support around a circumferential surface of a cylinder and floating and supporting the support by supplying the hot drying air from the circumferential surface of the cylinder to the coating film.
According to the present invention, since second-stage drying, which is full-scale drying, is performed in the helical air cushion drying step, after the coating film has been cured to some extent by the gelation of the coating film in the chilling-zone step, and first-stage drying in the plane air cushion drying step, liquid scattering from the surface of the coating film can be prevented in drying even if the binder has the characteristics of being difficult to cure as in the coating film for the thermal-developable light-sensitive material. Thereby, good surface condition of the coating film and good photographic performance can be achieved.
In the plane air cushion drying step, the wind velocity of drying air is preferably within a range between 20 m/min and 30 m/sec.
For an optimal range of the cold air temperature in the chilling-zone, and the drying air temperature in non-contact drying zone, setting the dry-bulb temperature in the chilling-zone within a range between 5xc2x0 C. and 50xc2x0 C. is preferable. It is also preferable to set the dry-bulb temperature in the constant-period of drying in first-stage and second-stage drying within the range between 25xc2x0 C. and 100xc2x0 C., and higher than the above-described dry-bulb temperature in the chilling-zone; and to set the wet-bulb temperature within the range between 10xc2x0 C. and 50xc2x0 C.
It is preferable that the dry-bulb temperature and the wet-bulb temperature are gradually lowered as the support is conveyed from the entrance side of the plane air cushion drying step toward the exit side of the helical air cushion drying step. Thereby, better surface condition of the coating film and better photographic performance can be achieved.
For an optimal time range from application to dry point, the dry point of the coating film is preferably within 300 seconds after the support is coated with the coating liquid.
For an optimal humidity-controlling time, the humidity-controlling time from the dry point until the support is wound with the winding device is preferably within a range between 10 seconds and 200 seconds.
The coating speed, that is an optimal speed when the support is conveyed from the coating step to the drying step is preferably within a range between 100 m/min and 300 m/min.